The present invention is directed to refrigeration devices, and, more particularly, to solid state thermoelectric refrigeration devices suitable for cooling optical radiation detectors.
Many electronic devices, such as optical radiation detectors, operate properly at temperatures substantially below ambient room temperature. Some types of very low light level charge-coupled device (CCD) detectors, for example, operate well only at temperatures of about -60.degree. Centigrade. Low light level CCD detectors are commonly used in connection with deep space observational astronomy.
Because of this requirement for sub-zero temperature operation, a number of types of refrigeration devices have been developed for cooling electronic circuits. One type of refrigeration device suitable for this use is based on the thermoelectric or Peltier cooling effect, by which heat is transferred across a junction of two semiconductors of dissimilar conductivity by passing a current through the junction. Thermoelectric refrigeration devices of this type typically include one or more cooling stages, each stage including an array of small individual semiconducting cooling elements, electrically connected in series and arranged so as to form two generally flat surfaces. When an electrical current is passed through the array, one of these surfaces is cooled and the other is heated. The heated surface has a generally greater heat density than does the cooled surface.
Inherent limitations in the heat pumping capacity and efficiency of thermoelectric refrigeration devices have previously limited the use of such devices to applications requiring only a modest amount of heat pumping, at temperatures just slightly below ambient. To achieve colder temperatures, thermoelectric refrigeration devices have typically been used along with some other type of refrigeration device to pre-cool the thermoelectric device and to dissipate waste heat. Thus, thermoelectric cooling devices have previously been employed to refrigerate optical detectors such as low light level CCD detectors, but only when used in connection with an additional refrigeration device, such as an ethylene glycol gas expansion type refrigerator.
Combined refrigeration devices of this sort, however, suffer from a number of shortcomings. The addition of an ethylene-glycol refrigerator, for example, obviates many of the special advantages derived from employing an entirely solid state thermoelectric refrigeration device. Whereas the thermoelectric refrigerator device typically has a long operational life that is virtually free of maintenance, an ethylene glycol refrigerator typically requires repeated maintenance throughout a relatively shorter operational life span. In addition, the need to merge together two different types of refrigeration devices leads to undue complexity.
Accordingly, there still exists a need for a thermoelectric refrigeration apparatus suitable for cooling electronic circuits, such as low light level CCD detectors without augmented cooling from another refrigeration device. The present invention fulfills this need.